Wenhao Shu

Reflection-Reduced Two-Layer Grating With Nearly 100% Diffraction Efficiency

A novel reflection-reduced two-layer grating is described with nearly 100% diffraction efficiency. The efficiency of the conventional grating should be improved, or some reported high-efficiency grating can work only for one polarization. The reflection-reduced grating can achieve high efficiency with a covering layer on the surface-relief grating. In addition, the two-layer grating can have wideband property compared with the single-layer grating. The presented novel grating can have merits of high efficiency of reflection-reduced grating and wideband property of two-layer grating. The modal method is applied to analyze the physical mechanism of high efficiency for both TE and TM polarizations. With the optimized grating parameters, efficiencies of 99.69% and 99.64% can be diffracted into the first order for the TE and TM polarizations, respectively. The moderate tolerance should make it possible to be fabricated easily for such a reflection-reduced two-layer grating, which can achieve nearly 100% diffraction efficiency for both the TE and TM polarizations.

Encapsulated grating for three-port beam splitter in reflection

An encapsulated grating with a metal slab is designed as a reflection three-port beam splitter at the wavelength of 1550 nm under normal incidence. Such a new grating is aimed to separate energies into the ±1st and the 0th orders for both TE and TM polarizations. The grating parameters such as grating period, duty cycle and grating depth are optimized by using rigorous coupled-wave analysis. Based on optimized grating parameters, efficiencies can reach more than 32% with the polarization-independent property. It indicates that reflection three-port beam splitter with high efficiency can be obtained by the encapsulated grating. Moreover, the presented reflection three-port grating has advantages of wide incident wavelength range and angular bandwidth, which would be useful in practical application.

Improving the extinction ratio by a novel sandwiched two-layer grating polarizer

The high efficiency and the wideband properties are not easy to be obtained by the conventional binary grating-based polarizer. Although the grating polarizer was demonstrated in experiments, the performance should be improved further to meet the practical applications. A novel sandwiched two-layer grating polarizer is presented to improve the efficiency and the bandwidth. Such a polarizer can have advantages of high efficiency of the sandwiched grating and wide bandwidth of the two-layer grating. The grating depths of two layers are optimized for the special duty cycle of 0.3 and the given period. The diffraction efficiency and the incident bandwidth of the novel grating polarizer are improved greatly compared with the conventional simple grating and the sandwiched single-layer grating. Moreover, high extinction ratio can be shown in both two orders and the moderate fabrication tolerance should be good guideline for practical applications.

Physical mechanism of beam splitting based on reflective embedded double-layer grating

It is not easy to achieve high performance for conventional beam splitters, such as high efficiency, good uniformity, polarization-independence, and wide bandwidth. A reflective embedded double-layer grating is described for beam splitting. With optimized grating profiles, the novel beam splitter can diffract both TE and TM polarizations into two orders with high performance. For the easy production, the fabrication tolerance is investigated and given. Most importantly, efficiencies more than 45% can be split into two orders within the wide bandwidth of 1412–1647 nm for TE polarization. The beam splitter based on multilayer coatings is sensitive to the incident angle and wavelength. And the bandwidth needs to be improved for the beam splitter based on simple grating. The design is of benefit for the performance improvement of the beam splitter by new grating configuration compared with the conventional simple grating.

Investigation on multilayer microstructure grating for three-port splitting

A new structure of microstructure reflection three-port beam splitter grating is described in this paper. The grating includes two dielectric layers and a metal slab on the substrate, where incident waves are reflected into the zeroth-order and the ± first-order with polarization-independent property. With the optimized grating profile, reflection efficiencies’ ratios between the first-order and the zeroth-order can reach 0.998 and 1.001 for TE and TM polarizations, respectively. Especially, the reflection grating can diffract efficiencies more than 30% into the ± first-order and the zeroth-order with the incident angular bandwidth of −1.9–1.9∘ for TM polarization, which can have merits compared with single-layer transmission grating.

Reflective three-port high-efficiency grating with two dielectric layers based on a sandwiched configuration

In this paper, we describe a novel reflective sandwiched three-port grating with two dielectric layers. The two-layer sandwiched grating can separate incident wave into the ± 1 and the 0th-order with high-efficiency beam splitting and good splitting ratios for both transverse electric (TE) and transverse magnetic (TM) polarizations. The grating parameters can be optimized by using rigorous coupled-wave analysis (RCWA) with a special duty cycle of 0.6. With the optimized results, efficiencies more than 32% in the ± 1st-orders and the 0th-order can be obtained. Furthermore, performance of the incident bandwidth and aspect ratio can be improved. Compared with conventional surface-relief grating, the grating with sandwiched structure is aimed at cleaning and protecting grating surface. The presented reflective two-layer sandwiched three-port grating would be put into practical applications for its beneficial performances.